1. Field of the Invention
The present invention relates generally to communications networking and more specifically to synchronizing bit-rate sampled data transmissions in a communications network.
2. Related Art
Advances in Voice over Internet Protocol (VOIP) technology and systems have resulted in VoIP telephony becoming the technology of choice for many telephony carriers. In VoIP systems, digital signal processors are used to digitize voice calls by taking periodic samples of the traffic. These samples are then applied to an analog to digital converter. The digitized samples are then arranged into a packet. In a cable modem system, these packets are further processed by the media access controller (MAC) of a cable modem for eventual transmission through the network.
Timing or latency issues are important for voice applications in a packet based transport network. In order to minimize latency, some applications provide an indication of transmission bandwidth availability to the VoIP processing agent. In this way, the VoIP processing agent is able to synchronize its operation with the expected availability of transmission bandwidth. A method for providing such an indication is described in commonly owned U.S. patent application Ser. No. 09/501,850, filed Feb. 10, 2000, now pending, and is incorporated by reference herein in its entirety. The method described in the above application, however, relies upon a parallel style interface. More specifically, the interface relies upon multiple pins to convey signals to the VoIP processing agent. For example, in the case where a bandwidth grant is received, five pins might be required to communicate the vector identifying the queue for which the grant has been issued. A parallel interface works well where the cost of multiple parallel signals is not an issue, such as in a large ASIC where both the DOCSIS MAC and VoIP processing agent are integrated. However, as the voice product market changes and expands, configurations of products have emerged where the DOCSIS MAC and voice processing agents are distributed into separate integrated circuits. Despite the distributed functionality, it is still necessary to provide packet sync information between the MAC integrated circuits and the VoIP processing agent integrated circuits.
Therefore, in order to minimize the cost of such integrated circuits, a need exists to reduce the number of pins on each device. More specifically, a need exists for a serial encoding protocol which allows packet sync information to be conveyed via a single pin on each integrated circuit.